Acquiring the ability to selectively produce interferon gamma (IFNgamma) or interleukin 4 (lL4) is a fundamental property of the immune system and enables T cell subsets (T helper 1, TH1, T helper 2, TH2) to deliver their effector functions. While the accumulated data clearly validate the polarization paradigm, the molecular mechanisms which control differentiation of naive T cells into memory TH1 or TH2 cells are not well understood. Much of what is known about regulation of gene transcription and the activity of individual response elements is derived from studies using immortalized cell lines. Very little is known about the regulation of transcriptional elements in primary cells nor about how transcriptional activity is regulated as primary cells differentiate or respond to external stimuli. This is largely due to the lack of an experimental system which permits investigation of promoter-directed transcriptional activity in primary cells. To address these questions, a novel experimental system will be employed. This system utilizes transgenic mice which express the luciferase gene under the control of a) proximal (prox. b-ZlP[IFNgamma]) and b) distal (dist. b-ZIP[IFNgamma]) response elements from the IFNgamma promoter, which bind b-ZIP transcription factors, c) the -538 to + 64 bp IFNgamma promoter, and d) a response element from the lL4 promoter which binds NF-AT/AP-1 transcription factors. The hypothesis to be tested is that acquisition of memory results from changes in transcriptional activity. The specific aims will focus on a) analyzing changes in transcriptional activity as naive T cells differentiate into effector T cells, b) determining how modulation of gene expression alters transcriptional activity, c) identifying transcription factors required for transcriptional activity, and d) determining if genetic regulation of cytokine production is reflected at the level of transcriptional activity. The long term goals of this project are to understand the molecular events which prevent naive T cells from producing IFNgamma and IL4 and which allow memory T cells to selectively produce these cytokines and to identify the genetic loci which control the development of TH1 or TH2 immunity. In a more general sense, these studies will examine changes in transcriptional activity as cells differentiate in a natural environment and acquire new properties. The immune-based pathology associated with many infectious diseases, including HIV infection, may result from overexpression of lL4 and the pathology associated with autoimmune diseases may result from overexpression of IFNgamma. Understanding regulation of cytokine gene expression may make it possible to correct overexpression of these genes and alleviate pathology associated with these diseases.